#define JPEG_INTERNALS
#include "jinclude.h"
#include "jpeglib.h"
#include "jdct.h"		/* Private declarations for DCT subsystem */

#ifdef DCT_IFAST_SUPPORTED


/*
   This module is specialized to the case DCTSIZE = 8.
*/

#if DCTSIZE != 8
Sorry, this code only copes with 8x8 DCTs. /* deliberate syntax err */
#endif


/* Scaling decisions are generally the same as in the LL&M algorithm;
   see jidctint.c for more details.  However, we choose to descale
   (right shift) multiplication products as soon as they are formed,
   rather than carrying additional fractional bits into subsequent additions.
   This compromises accuracy slightly, but it lets us save a few shifts.
   More importantly, 16-bit arithmetic is then adequate (for 8-bit samples)
   everywhere except in the multiplications proper; this saves a good deal
   of work on 16-bit-int machines.

   The dequantized coefficients are not integers because the AA&N scaling
   factors have been incorporated.  We represent them scaled up by PASS1_BITS,
   so that the first and second IDCT rounds have the same input scaling.
   For 8-bit JSAMPLEs, we choose IFAST_SCALE_BITS = PASS1_BITS so as to
   avoid a descaling shift; this compromises accuracy rather drastically
   for small quantization table entries, but it saves a lot of shifts.
   For 12-bit JSAMPLEs, there's no hope of using 16x16 multiplies anyway,
   so we use a much larger scaling factor to preserve accuracy.

   A final compromise is to represent the multiplicative constants to only
   8 fractional bits, rather than 13.  This saves some shifting work on some
   machines, and may also reduce the cost of multiplication (since there
   are fewer one-bits in the constants).
*/

#if BITS_IN_JSAMPLE == 8
#define CONST_BITS  8
#define PASS1_BITS  2
#else
#define CONST_BITS  8
#define PASS1_BITS  1		/* lose a little precision to avoid overflow */
#endif

/* Some C compilers fail to reduce "FIX(constant)" at compile time, thus
   causing a lot of useless floating-point operations at run time.
   To get around this we use the following pre-calculated constants.
   If you change CONST_BITS you may want to add appropriate values.
   (With a reasonable C compiler, you can just rely on the FIX() macro...)
*/

#if CONST_BITS == 8
#define FIX_1_082392200  ((JPEG_INT32)  277)		/* FIX(1.082392200) */
#define FIX_1_414213562  ((JPEG_INT32)  362)		/* FIX(1.414213562) */
#define FIX_1_847759065  ((JPEG_INT32)  473)		/* FIX(1.847759065) */
#define FIX_2_613125930  ((JPEG_INT32)  669)		/* FIX(2.613125930) */
#else
#define FIX_1_082392200  FIX(1.082392200)
#define FIX_1_414213562  FIX(1.414213562)
#define FIX_1_847759065  FIX(1.847759065)
#define FIX_2_613125930  FIX(2.613125930)
#endif


/* We can gain a little more speed, with a further compromise in accuracy,
   by omitting the addition in a descaling shift.  This yields an incorrectly
   rounded result half the time...
*/

#ifndef USE_ACCURATE_ROUNDING
#undef DESCALE
#define DESCALE(x,n)  RIGHT_SHIFT(x, n)
#endif


/* Multiply a DCTELEM variable by an INT32 constant, and immediately
   descale to yield a DCTELEM result.
*/

#define MULTIPLY(var,const)  ((DCTELEM) DESCALE((var) * (const), CONST_BITS))


/* Dequantize a coefficient by multiplying it by the multiplier-table
   entry; produce a DCTELEM result.  For 8-bit data a 16x16->16
   multiplication will do.  For 12-bit data, the multiplier table is
   declared INT32, so a 32-bit multiply will be used.
*/

#if BITS_IN_JSAMPLE == 8
#define DEQUANTIZE(coef,quantval)  (((IFAST_MULT_TYPE) (coef)) * (quantval))
#else
#define DEQUANTIZE(coef,quantval)  \
  DESCALE((coef)*(quantval), IFAST_SCALE_BITS-PASS1_BITS)
#endif


/* Like DESCALE, but applies to a DCTELEM and produces an int.
   We assume that int right shift is unsigned if INT32 right shift is.
*/

#ifdef RIGHT_SHIFT_IS_UNSIGNED
#define ISHIFT_TEMPS	DCTELEM ishift_temp;
#if BITS_IN_JSAMPLE == 8
#define DCTELEMBITS  16		/* DCTELEM may be 16 or 32 bits */
#else
#define DCTELEMBITS  32		/* DCTELEM must be 32 bits */
#endif
#define IRIGHT_SHIFT(x,shft)  \
  ((ishift_temp = (x)) < 0 ? \
   (ishift_temp >> (shft)) | ((~((DCTELEM) 0)) << (DCTELEMBITS-(shft))) : \
   (ishift_temp >> (shft)))
#else
#define ISHIFT_TEMPS
#define IRIGHT_SHIFT(x,shft)	((x) >> (shft))
#endif

#ifdef USE_ACCURATE_ROUNDING
#define IDESCALE(x,n)  ((int) IRIGHT_SHIFT((x) + (1 << ((n)-1)), n))
#else
#define IDESCALE(x,n)  ((int) IRIGHT_SHIFT(x, n))
#endif

void jpeg_idct_ifast( j_decompress_ptr cinfo, jpeg_component_info * compptr,
                      JCOEFPTR coef_block,
                      JSAMPARRAY output_buf, JDIMENSION output_col ) {
  DCTELEM tmp0, tmp1, tmp2, tmp3, tmp4, tmp5, tmp6, tmp7;
  DCTELEM tmp10, tmp11, tmp12, tmp13;
  DCTELEM z5, z10, z11, z12, z13;
  JCOEFPTR inptr;
  IFAST_MULT_TYPE * quantptr;
  int * wsptr;
  JSAMPROW outptr;
  JSAMPLE *range_limit = IDCT_range_limit( cinfo );
  int ctr;
  int workspace[DCTSIZE2];	/* buffers data between passes */
  SHIFT_TEMPS			/* for DESCALE */
  ISHIFT_TEMPS			/* for IDESCALE */
  /* Pass 1: process columns from input, store into work array. */
  inptr = coef_block;
  quantptr = ( IFAST_MULT_TYPE * ) compptr->dct_table;
  wsptr = workspace;
  for( ctr = DCTSIZE; ctr > 0; ctr-- ) {
    /* Due to quantization, we will usually find that many of the input
       coefficients are zero, especially the AC terms.  We can exploit this
       by short-circuiting the IDCT calculation for any column in which all
       the AC terms are zero.  In that case each output is equal to the
       DC coefficient (with scale factor as needed).
       With typical images and quantization tables, half or more of the
       column DCT calculations can be simplified this way.
    */
    if( inptr[DCTSIZE * 1] == 0 && inptr[DCTSIZE * 2] == 0 &&
        inptr[DCTSIZE * 3] == 0 && inptr[DCTSIZE * 4] == 0 &&
        inptr[DCTSIZE * 5] == 0 && inptr[DCTSIZE * 6] == 0 &&
        inptr[DCTSIZE * 7] == 0 ) {
      /* AC terms all zero */
      int dcval = ( int ) DEQUANTIZE( inptr[DCTSIZE * 0], quantptr[DCTSIZE * 0] );
      wsptr[DCTSIZE * 0] = dcval;
      wsptr[DCTSIZE * 1] = dcval;
      wsptr[DCTSIZE * 2] = dcval;
      wsptr[DCTSIZE * 3] = dcval;
      wsptr[DCTSIZE * 4] = dcval;
      wsptr[DCTSIZE * 5] = dcval;
      wsptr[DCTSIZE * 6] = dcval;
      wsptr[DCTSIZE * 7] = dcval;
      inptr++;			/* advance pointers to next column */
      quantptr++;
      wsptr++;
      continue;
    }
    /* Even part */
    tmp0 = DEQUANTIZE( inptr[DCTSIZE * 0], quantptr[DCTSIZE * 0] );
    tmp1 = DEQUANTIZE( inptr[DCTSIZE * 2], quantptr[DCTSIZE * 2] );
    tmp2 = DEQUANTIZE( inptr[DCTSIZE * 4], quantptr[DCTSIZE * 4] );
    tmp3 = DEQUANTIZE( inptr[DCTSIZE * 6], quantptr[DCTSIZE * 6] );
    tmp10 = tmp0 + tmp2;	/* phase 3 */
    tmp11 = tmp0 - tmp2;
    tmp13 = tmp1 + tmp3;	/* phases 5-3 */
    tmp12 = MULTIPLY( tmp1 - tmp3, FIX_1_414213562 ) - tmp13; /* 2*c4 */
    tmp0 = tmp10 + tmp13;	/* phase 2 */
    tmp3 = tmp10 - tmp13;
    tmp1 = tmp11 + tmp12;
    tmp2 = tmp11 - tmp12;
    /* Odd part */
    tmp4 = DEQUANTIZE( inptr[DCTSIZE * 1], quantptr[DCTSIZE * 1] );
    tmp5 = DEQUANTIZE( inptr[DCTSIZE * 3], quantptr[DCTSIZE * 3] );
    tmp6 = DEQUANTIZE( inptr[DCTSIZE * 5], quantptr[DCTSIZE * 5] );
    tmp7 = DEQUANTIZE( inptr[DCTSIZE * 7], quantptr[DCTSIZE * 7] );
    z13 = tmp6 + tmp5;		/* phase 6 */
    z10 = tmp6 - tmp5;
    z11 = tmp4 + tmp7;
    z12 = tmp4 - tmp7;
    tmp7 = z11 + z13;		/* phase 5 */
    tmp11 = MULTIPLY( z11 - z13, FIX_1_414213562 ); /* 2*c4 */
    z5 = MULTIPLY( z10 + z12, FIX_1_847759065 ); /* 2*c2 */
    tmp10 = MULTIPLY( z12, FIX_1_082392200 ) - z5; /* 2*(c2-c6) */
    tmp12 = MULTIPLY( z10, - FIX_2_613125930 ) + z5; /* -2*(c2+c6) */
    tmp6 = tmp12 - tmp7;	/* phase 2 */
    tmp5 = tmp11 - tmp6;
    tmp4 = tmp10 + tmp5;
    wsptr[DCTSIZE * 0] = ( int )( tmp0 + tmp7 );
    wsptr[DCTSIZE * 7] = ( int )( tmp0 - tmp7 );
    wsptr[DCTSIZE * 1] = ( int )( tmp1 + tmp6 );
    wsptr[DCTSIZE * 6] = ( int )( tmp1 - tmp6 );
    wsptr[DCTSIZE * 2] = ( int )( tmp2 + tmp5 );
    wsptr[DCTSIZE * 5] = ( int )( tmp2 - tmp5 );
    wsptr[DCTSIZE * 4] = ( int )( tmp3 + tmp4 );
    wsptr[DCTSIZE * 3] = ( int )( tmp3 - tmp4 );
    inptr++;			/* advance pointers to next column */
    quantptr++;
    wsptr++;
  }
  /* Pass 2: process rows from work array, store into output array. */
  /* Note that we must descale the results by a factor of 8 == 2**3, */
  /* and also undo the PASS1_BITS scaling. */
  wsptr = workspace;
  for( ctr = 0; ctr < DCTSIZE; ctr++ ) {
    outptr = output_buf[ctr] + output_col;
    /* Rows of zeroes can be exploited in the same way as we did with columns.
       However, the column calculation has created many nonzero AC terms, so
       the simplification applies less often (typically 5% to 10% of the time).
       On machines with very fast multiplication, it's possible that the
       test takes more time than it's worth.  In that case this section
       may be commented out.
    */
    #ifndef NO_ZERO_ROW_TEST
    if( wsptr[1] == 0 && wsptr[2] == 0 && wsptr[3] == 0 && wsptr[4] == 0 &&
        wsptr[5] == 0 && wsptr[6] == 0 && wsptr[7] == 0 ) {
      /* AC terms all zero */
      JSAMPLE dcval = range_limit[IDESCALE( wsptr[0], PASS1_BITS + 3 )
                                            & RANGE_MASK];
      outptr[0] = dcval;
      outptr[1] = dcval;
      outptr[2] = dcval;
      outptr[3] = dcval;
      outptr[4] = dcval;
      outptr[5] = dcval;
      outptr[6] = dcval;
      outptr[7] = dcval;
      wsptr += DCTSIZE;		/* advance pointer to next row */
      continue;
    }
    #endif
    /* Even part */
    tmp10 = ( ( DCTELEM ) wsptr[0] + ( DCTELEM ) wsptr[4] );
    tmp11 = ( ( DCTELEM ) wsptr[0] - ( DCTELEM ) wsptr[4] );
    tmp13 = ( ( DCTELEM ) wsptr[2] + ( DCTELEM ) wsptr[6] );
    tmp12 = MULTIPLY( ( DCTELEM ) wsptr[2] - ( DCTELEM ) wsptr[6], FIX_1_414213562 )
            - tmp13;
    tmp0 = tmp10 + tmp13;
    tmp3 = tmp10 - tmp13;
    tmp1 = tmp11 + tmp12;
    tmp2 = tmp11 - tmp12;
    /* Odd part */
    z13 = ( DCTELEM ) wsptr[5] + ( DCTELEM ) wsptr[3];
    z10 = ( DCTELEM ) wsptr[5] - ( DCTELEM ) wsptr[3];
    z11 = ( DCTELEM ) wsptr[1] + ( DCTELEM ) wsptr[7];
    z12 = ( DCTELEM ) wsptr[1] - ( DCTELEM ) wsptr[7];
    tmp7 = z11 + z13;		/* phase 5 */
    tmp11 = MULTIPLY( z11 - z13, FIX_1_414213562 ); /* 2*c4 */
    z5 = MULTIPLY( z10 + z12, FIX_1_847759065 ); /* 2*c2 */
    tmp10 = MULTIPLY( z12, FIX_1_082392200 ) - z5; /* 2*(c2-c6) */
    tmp12 = MULTIPLY( z10, - FIX_2_613125930 ) + z5; /* -2*(c2+c6) */
    tmp6 = tmp12 - tmp7;	/* phase 2 */
    tmp5 = tmp11 - tmp6;
    tmp4 = tmp10 + tmp5;
    /* Final output stage: scale down by a factor of 8 and range-limit */
    outptr[0] = range_limit[IDESCALE( tmp0 + tmp7, PASS1_BITS + 3 )
                            & RANGE_MASK];
    outptr[7] = range_limit[IDESCALE( tmp0 - tmp7, PASS1_BITS + 3 )
                            & RANGE_MASK];
    outptr[1] = range_limit[IDESCALE( tmp1 + tmp6, PASS1_BITS + 3 )
                            & RANGE_MASK];
    outptr[6] = range_limit[IDESCALE( tmp1 - tmp6, PASS1_BITS + 3 )
                            & RANGE_MASK];
    outptr[2] = range_limit[IDESCALE( tmp2 + tmp5, PASS1_BITS + 3 )
                            & RANGE_MASK];
    outptr[5] = range_limit[IDESCALE( tmp2 - tmp5, PASS1_BITS + 3 )
                            & RANGE_MASK];
    outptr[4] = range_limit[IDESCALE( tmp3 + tmp4, PASS1_BITS + 3 )
                            & RANGE_MASK];
    outptr[3] = range_limit[IDESCALE( tmp3 - tmp4, PASS1_BITS + 3 )
                            & RANGE_MASK];
    wsptr += DCTSIZE;		/* advance pointer to next row */
  }
}

#endif /* DCT_IFAST_SUPPORTED */
